Alkaline storage battery

ABSTRACT

An alkaline storage battery of the present invention includes a battery case and a group of electrodes. The battery case is provided with a resin case and a coating layer made of a resin formed on at least one surface selected from an inner surface and an outer surface of the resin case. The hydrogen permeability coefficient of the resin that is the material of the coating layer is 1×10 −15  mol·m/m 2 ·sec·Pa or less.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to alkaline storage batteries.

[0003] 2. Description of the Related Art

[0004] An enclosed alkaline battery using a battery case often is usedas a power source for large scale power, for example, a power source ofelectric cars or hybrid cars. In such an enclosed alkaline battery, whenan electrolyte or a gas component permeates through the battery case andleaks out, the characteristics deteriorate significantly. In order toprevent this leakage, in general, a battery case made of a metal isused.

[0005] However, it is difficult to form the battery case made of a metalinto an arbitrary shape, and the battery case made of a metal is heavy.On the other hand, although a battery case made of a resin can beprocessed easily and is light, vapor or oxygen gas or hydrogen gas canpermeate through the battery case easily. In particular, in anickel-metal hydride battery using a hydrogen-absorbing alloy, when theamount of the hydrogen in the battery case is reduced by the hydrogenpermeating through the battery case, the capacity balance between thepositive electrode and the negative electrode is broken, which maydeteriorate the characteristics significantly.

[0006] In order to solve this problem, a method for forming a metallayer on the surface of a battery bath made of a resin is proposed(Japanese Patent No. 3049854). However, this method is not preferable,for example, in view of the possibility of short-circuiting because themetal layer is exposed at the surface of the battery case.

SUMMARY OF THE INVENTION

[0007] Therefore, with the foregoing in mind, it is an object of thepresent invention to provide an alkaline storage battery including abattery case made primarily of a resin and having reduced deteriorationof the battery characteristics.

[0008] In order to achieve the above object, a first alkaline storagebattery of the present invention includes a battery case and a group ofelectrodes arranged in the battery case and is characterized in that thebattery case includes a resin case and a coating layer made of a resinformed on at least one surface selected from an inner surface and anouter surface of the resin case, and the hydrogen permeabilitycoefficient of the resin that is the material of the coating layer is1×10⁻¹⁵ mol·m/m²·sec·Pa or less. In this alkaline storage battery, thecoating layer made of a resin having a low hydrogen permeabilitycoefficient is formed so that hydrogen gas or the like is suppressedfrom permeating through the battery case to the outside, and thereforethe deterioration of the characteristics can be suppressed.

[0009] The hydrogen permeability coefficient can be measured using ageneral method. The values of the hydrogen permeability coefficientdescribed in the examples of this specification are obtained as a resultof measurement using a method defined in the method A of JIS-K7126 andsetting the test temperature to 40° C.

[0010] In the first alkaline storage battery, it is preferable that theresin of the coating layer is at least one resin selected from the groupconsisting of polyvinyl alcohol, ethylene-vinyl alcohol copolymer,polyacrylonitrile and polyvinylidene chloride. These resins arepreferable because their hydrogen permeability coefficients aresufficiently low.

[0011] In the first alkaline storage battery, it is preferable that theresin case is made of a polymer alloy of polypropylene and polyphenyleneether. According to this embodiment, a resin case having excellentstrength, moldability, chemical resistance, and weather resistance canbe obtained.

[0012] In the first alkaline storage battery, it is preferable that thethickness of the coating layer is in the range from 5 μm to 100 μm.

[0013] In the first alkaline storage battery, it is preferable that thehydrogen permeability of the coating layer is 1×10⁻¹¹·mol/m² sec·Pa orless.

[0014] In the first alkaline storage battery, the coating layer may beformed on an outer surface of the resin case. The above alkaline storagebattery may include a multilayered film formed on the at least onesurface, and the multilayered film may include the coating layer.

[0015] In the first alkaline storage battery, it is preferable that themultilayered film is integrated with the resin case by insert molding ortwo-color molding. According to this embodiment, the adhesion betweenthe multilayered film and the resin case can be enhanced.

[0016] In the first alkaline storage battery, it is preferable that themultilayered film includes a surface layer made of a water resistantresin. According to this embodiment, an alkaline storage battery havingparticularly reduced deterioration of the battery characteristics underhigh humidity can be obtained.

[0017] In the first alkaline storage battery, it is preferable that themultilayered film includes a layer containing the same resin as a resinconstituting the resin case on a surface in contact with the resin case.According to this embodiment, the multilayered film can be suppressedfrom being detached from the resin case.

[0018] A second alkaline storage battery of the present inventionincludes a battery case and a group of electrodes arranged in thebattery case and is characterized in that the battery case includes aresin case and a multilayered film formed on at least one surfaceselected from an inner surface and an outer surface of the resin case,and the multilayered film includes a surface layer made of a resin and ametal layer disposed between the surface layer and the resin case. Inthis alkaline storage battery, the metal layer formed on the surface ofthe resin case of the multilayered film can suppress hydrogen gas or thelike from permeating through the battery case to the outside, andtherefore an alkaline storage battery having reduced deterioration ofthe battery characteristics can be obtained.

[0019] In the second alkaline storage battery, it is preferable that themultilayered film further includes a resin layer disposed between themetal layer and the resin case. It also is preferable that this resinlayer contains the same resin as the resin constituting the resin case.According to this embodiment, the metal layer is prevented from beingdetached from the resin case.

[0020] In the second alkaline storage battery, it is preferable that themultilayered film is integrated with the resin case by insert molding.

[0021] In the second alkaline storage battery, it is preferable that theresin case is made of a polymer alloy of polypropylene and polyphenyleneether.

[0022] In the second alkaline storage battery, it is preferable that themetal layer is made of aluminum. According to this embodiment, alightweight and relatively inexpensive alkaline storage battery can beobtained.

[0023] As described above, the alkaline storage battery of the presentinvention includes a battery case body formed primarily of a resin and acoating layer with which the battery case body is coated, and thehydrogen permeability coefficient of the coating layer is small. Byusing the battery case body formed primarily of a resin, an alkalinestorage battery having high safety and a small weight and an arbitraryshape can be produced. Furthermore, the coating layer having a smallhydrogen permeability coefficient makes it possible to suppress thedeterioration of the characteristics. The present invention can beapplied to alkaline storage batteries such as a nickel-metal hydridebattery or a nickel-cadmium storage battery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1A shows a top face of an alkaline storage battery of thepresent invention, and FIG. 1B shows the side face thereof.

[0025]FIG. 2 shows a partial cross-section of the alkaline storagebattery shown in FIG. 1.

[0026]FIG. 3 shows a cross-section of a group of electrodes of thealkaline storage battery shown in FIG. 1.

[0027]FIG. 4 shows a partial cross-section of an example of the body ofa battery case of the alkaline storage battery of the present invention.

[0028]FIG. 5 shows a partial cross-section of another example of thebody of a battery case of the alkaline storage battery of the presentinvention.

[0029]FIG. 6 shows a partial cross-section of yet another example of thebody of a battery case of the alkaline storage battery of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, embodiments of the present invention will bedescribed with reference to the accompanying drawings.

[0031] Embodiment 1

[0032] In Embodiment 1, an example of an alkaline storage battery of thepresent invention will be described. FIG. 1A is a top plan view of analkaline storage battery 10 of Embodiment 1, and FIG. 1B is a side viewthereof.

[0033] The alkaline storage battery 10 is provided with a battery case12 including a battery case body 11 and a lid 11 a enclosing the batterycase body 11. A safety valve 13, a lid 14 with a communicating hole anda temperature sensor mounting hole 15 are provided in the lid 11 a. Twoterminals 16 are provided in the battery case body 11. The safety valve13 is open when the internal pressure in the battery case 12 reaches apredetermined value or more, and the gas inside is released so as toreduce the internal pressure in the battery case 12. A plurality ofprotrusions are formed on the surface of the battery case body 11 inorder to improve the heat release properties when a plurality ofalkaline storage batteries 10 are arranged while being attached tightlyto each other. FIG. 2 is a partial cross-sectional view taken along lineI-I of FIG. 1A.

[0034] The internal portion of the battery case body 11 is partitionedinto six compartments by partitions 11 b. A group of electrodes 20 andan electrolyte (not shown) are disposed in each compartment. The groupof electrodes 20 and the electrolyte constitute a cell 17. In otherwords, the alkaline storage battery 10 is provided with six cells 17.The lid 14 with a communicating hole makes it possible to balance theinternal pressure in the cells 17.

[0035]FIG. 3 is a cross-sectional view of the group of electrodes 20.The group of electrodes 20 includes a separator 21, a positive plate 22and a negative plate 23 that are laminated alternately with theseparator 21 interposed therebetween, a collector 24 connected to thepositive plate 22 and a collector 25 connected to the negative plate 23.As shown in FIG. 2, the collectors 24 and 25 are connected to theterminal 16 or a connection terminal 26. The collector 25 of the cell 17is connected to the collector 24 of the adjacent cell 17 via theconnection terminal 26. Thus, the cells 17 are connected in series.

[0036] For the separator 21, a commonly used separator can be used, andfor example, a polypropylene nonwaven fabric that has been treated so asto be hydrophilic can be used. For the positive plate 22 and thenegative plate 23, an electrode plate that is commonly used for analkaline storage battery can be used. For example, the positive plate 22can be produced by applying a paste containing nickel hydroxide as anactive material to a conductive support member so as to produce a sheet,and then drying, rolling and cutting this sheet. The negative plate 23can be produced by applying a paste containing a hydrogen-absorbingalloy or cadmium hydroxide to a conductive support member so as toproduce a sheet, and then drying, rolling and cutting this sheet.

[0037] Next, the battery case body 11 will be described. The batterycase body 11 includes a resin case, and a coating layer made of a resinformed on at least one surface selected from the inner surface and theouter surface of the resin case. FIG. 4 shows a partial cross-section ofa battery case body 41 in which a coating layer is formed on the outersurface of a resin case as an example of the battery case body 11.

[0038] Referring to FIG. 4, the battery case body 41 includes a resincase 42 and a coating layer 43 that is formed on the outer surface ofthe resin case 42. The resin case 42 is a case made of a resin or a casemade primarily of a resin. The thicker the resin case 42 is, the higherthe strength is and the lower the gas permeability is, but in this case,the weight becomes larger. When the resin case 42 is thick, the heatrelease properties of the battery deteriorate. For this reason, ingeneral, the average thickness of the resin case 42 is about 1 mm to 3mm. The resin case 42 is formed of a resin, such as polypropylene (PP)alone, or a polymer alloy of polypropylene (PP) and polyphenylene ether(PPE).

[0039] The coating layer 43 can be formed of a resin (hereinafter, alsoreferred to as “resin A”). The hydrogen permeability coefficient of theresin A is 1×10⁻¹⁵ mol·m/m²·sec·Pa or less, and preferably 1×10⁻¹⁷mol·m/m²·sec·Pa or less. For the resin A, at least one resin selectedfrom the group consisting of polyvinyl alcohol (PVA), ethylene-vinylalcohol copolymer (EvOH), polyacrylonitrile (PAN) and polyvinylidenechloride (PVDC) can be used. The thickness of the coating layer 43 is inthe range from 5 μm to 100 μm, and preferably in the range from 10 μm to50 μm. The coating layer 43 may be coated with an additional coatinglayer. The hydrogen permeability of the coating layer 43 is expressed byan equation (hydrogen permeability)=(hydrogen permeabilitycoefficient)/(thickness). It is preferable that the hydrogenpermeability of the coating layer 43 is 2×10⁻¹⁰ mol/m²·sec·Pa or less,more preferably 1×10⁻¹¹ mol/m²·sec·Pa or less.

[0040] Next, a battery case body 51 in which a multilayered filmincluding a coating layer is formed on the outer surface of a resin casewill be described as another example of the battery case body 11 withreference to FIG. 5. In this case, the battery case body 51 includes aresin case 42 and a multilayered film 53 formed on the outer surface ofthe resin case 42. The resin case 42 is the same as the resin case 42described above. The multilayered film 53 includes a first layer 53 a, asecond layer 53 b and a third layer 53 c that are arranged in this orderfrom the resin case 42 side. It is preferable to use a material having ahigh adhesion to the resin case 42 as the material of the first layer 53a, and the material preferably contains a resin constituting the resincase 42. There is no limitation regarding the thickness of the firstlayer 53 a, but it is for example, about 20 μm to 70 μm. The secondlayer 53 b is made of the same material (resin A) as the above-describedcoating layer 43, and has the same thickness. The third layer 53 c hasweather resistance and chemical resistance and is formed in order toprotect the second layer 53 b. The third layer 53 c, which is thesurface layer, preferably is formed of a moisture resistant resin, andfor example, can be formed of polypropylene (PP). There is no limitationregarding the thickness of the third layer 53 c, but it is for example,about 20 μm to 70 μm. It is sufficient that the multilayered film 53contains the second layer 53 b having a small hydrogen permeabilitycoefficient and there is no limitation regarding the number of layers.

[0041] Next, the lid 11 a will be described. The lid 11 a can be formedof the same material as the resin case 42. There is no limitationregarding the thickness of the lid 11 a, but in general, the averagethickness is about 2 mm to 4 mm. It is preferable that the coating layer43 or the multilayered film 53 also is formed in the lid 11 a. However,since the lid 11 a generally is thicker than the resin case 42, hydrogenor the like permeates through the lid only to a small extent, even ifthe coating layer is not formed.

[0042] In the alkaline storage battery of the present invention, it ispreferable that a coating layer having a low hydrogen permeabilitycoefficient is formed on the entire surface of the battery case body.However, even if the coating layer is not formed on the entire surface,a sufficient effect can be obtained if the coating layer is formed on aportion in which the thickness of the resin case is small and throughwhich hydrogen permeates easily.

[0043] Hereinafter, a method for producing the alkaline storage batteryof the present invention will be described. The alkaline storage batteryof the present invention can be produced in the same manner as whenproducing a commonly used alkaline storage battery except for how toproduce the battery case body. Therefore, a method for producing thebattery case body will be described.

[0044] First, a method for producing the battery case body 41 will bedescribed. The resin case 42 can be produced by a commonly used method,such as injection molding. The coating layer 43 can be formed byapplying a resin solution that is the material of the coating layer 43to the outer surface of the resin case 42 and drying the resin solution.The application and the drying can be repeated.

[0045] Next, a method for producing the battery case body 51 in whichthe coating layer is formed on the inner surface of the battery casebody will be described. The battery case body 51 can be formed by insertmolding or two-color molding. More specifically, the multilayered film53 is disposed inside the mold, and then a resin that is the material ofthe resin case 42 is injected for molding, so that the battery case body51 in which the multilayered film 53 is integrated with the innersurface of the resin case 42 can be produced.

[0046] As described above, in the alkaline storage battery of Embodiment1, the battery case body including the resin case and the coating layerhaving a small hydrogen permeability coefficient that is formed on thesurface of the resin case are used. In this case, the hydrogenpermeability of the battery case body provided with one coating layer isexpressed by Equation 1 below.

1/(the hydrogen permeability of the battery case body)=1/(the hydrogenpermeability of the resin case)+1/(the hydrogen permeability of thecoating layer)  Equation 1

[0047] Therefore, the hydrogen permeability of the battery case body canbe reduced significantly by forming the coating layer having a lowhydrogen permeability. In Embodiment 1, the hydrogen permeability hasbeen described, but gas other than hydrogen such as oxygen or anelectrolyte hardly permeates the coating layer having a low hydrogenpermeability, so that this embodiment can provide an effect ofpreventing permeation of these substances.

[0048] Embodiment 2

[0049] In Embodiment 2, another example of an alkaline storage batteryof the present invention will be described. The alkaline storage batteryof Embodiment 2 is different only in the coating layer formed on thebattery case body from the alkaline storage battery described inEmbodiment 1, so that duplicate description will be omitted.

[0050] The battery case body of Embodiment 2 includes the resin case 42described in Embodiment 1, and the multilayered film formed on at leastone surface selected from the inner surface and the outer surface of theresin case 42. The multilayered film includes a surface layer made of aresin and a metal layer disposed between the surface layer and the resincase 42. In other words, the multilayered film that coats the resin case42 includes a metal layer, and the surface layer made of a resinprevents the metal layer from being exposed to the surface.

[0051]FIG. 6 shows an enlarged view of a part of a battery case body 61in which a multilayered film 63 is formed on the outer surface of theresin case 42 as an example of the battery case body of Embodiment 2.The multilayered film 63 includes a surface layer 63 c made of a resin,a metal layer 63 b disposed between the surface layer 63 c and the resincase 42, and a layer 63 a disposed between the metal layer 63 b and theresin case 42. The surface layer 63 c is a layer that prevents the metallayer 63 b to be exposed, and for example, can be formed of a nylonresin or a polyolefin resin. It is preferable that the surface layer 63c is made of a moisture resistant resin. The metal layer 63 b can beformed of, for example, aluminum or iron. The layer 63 a is a layer forenhancing the adhesion between the multilayered film 63 and the resincase 42, and it preferably contains the same resin as the resinconstituting the resin case 42. For example, when the resin case 42contains polypropylene, the layer 63 a can be formed of polypropylene.The thickness of the metal layer 63 b is, for example, in the range from5 μm to 100 μm, preferably in the range from 20 μm to 50 μm. Thethickness of the surface layer 63 c is, for example, about 20 μm to 70μm. The thickness of the layer 63 a is, for example, about 20 μm to 70μm.

[0052] The battery case body 61 can be produced by insert molding ortwo-color molding in the same manner as when producing the battery casebody 51 of Embodiment 1. In this case, the multilayered film 63 isintegrated with the resin case 42 by insert molding or two-colormolding. There is no limitation regarding the number of layersconstituting the multilayered film, as long as the object of the presentinvention can be achieved. In FIG. 6, the multilayered film 63 is formedon the outer surface of the resin case, but the multilayered film 63 canbe formed on the inner surface of the resin case. Also in this case, themultilayered film 63 can be formed by insert molding or two-colormolding.

EXAMPLES

[0053] Hereinafter, the present invention will be described morespecifically by way of example.

Example 1

[0054] In Example 1, a nickel-metal hydride battery was produced as anexample of the alkaline storage battery of Embodiment 1. For thenickel-metal hydride battery of Example 1, the battery case body havingthe same structure as that of the battery case body 41 shown in FIG. 4was used.

[0055] For the separator 21, a sulfonated polypropylene nonwaven fabricwas used. A positive plate containing nickel hydroxide was used for thepositive plate 22 and a negative plate containing a hydrogen-absorbingalloy was used for the negative plate 23. For an electrolyte, analkaline aqueous solution having a specific gravity of about 1.3 thatcontains potassium hydroxide as the main solute was used.

[0056] The resin case 42 of the battery case body was formed of apolymer alloy of polypropylene (PP) and polyphenylene ether (PPE) byinjection molding. The hydrogen permeability coefficient of this polymeralloy was 4×10⁻¹⁵ mol/m/m²·sec·Pa. The average thickness of the resincase was 1.5 mm.

[0057] The coating layer made of ethylene-vinyl alcohol copolymer(EvOH), polyvinylidene chloride (PVDC), or polyvinyl alcohol was formed.More specifically, a solution in which these resins were dissolved in asolvent based on water or alcohol was applied onto the outer surface ofthe resin case and then dried, which process was repeated, so that thecoating layer was formed. In order to enhance the adhesion between theresin case and the coating layer for all the samples, the surface of theresin case was subjected to an anchor coating treatment before the resinsolution was applied in order to activate the surface.

[0058] With the above members, three types of nickel-metal hydridebatteries (capacity: 6.5 Ah) were produced. As a comparative sample A, anickel-metal hydride battery that was different only in that no coatinglayer was formed was produced. Then, these four batteries were chargedsuch that the state of charge (SOC) reached 80% and then were stored inan atmosphere at 65° C. for one month. Next, the amount of the dischargereserve of the negative electrode was measured with respect to thebatteries that had been stored. Herein, “discharge reserve” refers to anegative plate capacity that is charged greater than a positive platecapacity. It seems that when hydrogen is released from the inside of thebattery case to the outside, the partial pressure of hydrogen inside thebattery case is reduced, so that hydrogen is released from thehydrogen-absorbing alloy and therefore the discharge reserve is reduced.When the negative plate capacity is reduced and becomes equal to thepositive plate capacity or less (i.e., the discharge reserve is 0), thecharacteristics of the battery are deteriorated significantly.

[0059] The discharge reserve was measured in the following manner.First, the battery was discharged until the voltage of the batteryreached 1.0 V. Then, a hole was drilled on the upper portion of thebattery and an electrolyte was refilled. Then, a Hg/HgO referenceelectrode was immersed in the electrolyte in the battery case. Then, thebattery was overdischarged while the discharge capacity was measured.The discharge reserve was defined by an equation (the dischargereserve)=(the discharge capacity up to the point when the potentialdifference obtained by subtracting the potential of the referenceelectrode from the potential of the negative electrode reaches −0.7V)−(the discharge capacity up to the point when the voltage of the cellreaches 0 V). Table 1 shows the thickness of the coating layer of eachsample, the measurement results of the discharge capacity, and thehydrogen permeability coefficient of the resin constituting each coatinglayer. TABLE 1 hydrogen permeability thickness of coefficient materialof coating layer discharge [mol · m/m² · Sample No. coating layer [μm]reserve [Ah] sec · Pa] Comparative No coating — 2.0 — Sample A layerSample 1 EvOH 7 2.4 8 × 10⁻¹⁸ Sample 2 PVDC 5 2.2 1 × 10⁻¹⁷ Sample 3 PVA10 2.6 6 × 10⁻¹⁸

[0060] As shown in Table 1, the sample provided with the coating layerhad a larger discharge reserve than that of Comparative Sample A. Thismeans that a reduction in the discharge reserve was small, that is, theamount of hydrogen that permeates through the battery case to theoutside was small. Thus, hydrogen was suppressed from permeating throughthe battery case by using the battery case in which the coating layermade of a resin having a small hydrogen permeability coefficient wasformed. Furthermore, the permeation of hydrogen was suppressed furtherby applying and drying the resin solution so as to form the coatinglayer, and then performing a heat treatment at a temperature of 130 to160° C. so as to increase the crystallinity of the resin constitutingthe coating layer.

Example 2

[0061] In Example 2, a nickel-metal hydride battery was produced as anexample of the alkaline storage batteries of Embodiments 1 and 2.

[0062] First, multilayered films were formed. A multilayered film ofsample 4 has a layer structure of polypropylene (PP)/ethylene-vinylalcohol copolymer (EvOH)/polyethylene (PE). A multilayered film ofsample 5 has a layer structure of polypropylene (PP) Al foil/nylon. Asdescribed in Example 1, EvOH is a resin having a small hydrogenpermeability coefficient. These multilayered films were formed by rollmolding or injection molding.

[0063] Then, the battery case body was produced by insert molding.First, the multilayered film as described above was disposed in a moldof the battery case body. Then a PP-PPE polymer alloy that is thematerial of the resin case was injected into the mold, so that thebattery case body provided with the resin case and the multilayered filmintegrated with the outer surface of the resin case was produced.

[0064] A nickel-metal hydride battery was produced in the same manner asin Example 1 except that the thus produced battery case body was used.As Comparative Sample B, a nickel-metal hydride battery was producedwith a battery case body that was not provided with the multilayeredfilm. Then, discharge, storage and measurement of the discharge reservewith respect to the produced nickel-metal hydride batteries wereperformed in the same manner as in Example 1. Table 2 shows themeasurement results and the thickness of each layer of the multilayeredfilm. In Table 2, the first layer is the layer attached to the resincase and the third layer is the surface layer. TABLE 2 material ofmultilayered film discharge first layer/second layer/ thickness ofreserve Sample No. third layer each layer [μm] [Ah] Comparative Nomultilayered film — 2.0 Sample B Sample 4 PP/EvOH/PE 70/20/30 2.7 Sample5 PP/Al foil/nylon 20/50/20 3.7

[0065] As shown in Table 2, Sample 4, which is an alkaline storagebattery of Embodiment 1, and Sample 5, which is an alkaline storagebattery of Embodiment 2, had a larger discharge reserve of ComparativeSample B. Thus, according to the alkaline storage batteries of thepresent invention, hydrogen is suppressed from permeating through thebattery case to the outside.

[0066] When Samples 1 and 3 of Example 1 were stored in an atmosphere ata temperature of 65° C. under high humidity (humidity: 80%) for onemonth and then the discharge reserve was measured, the discharge reservewas 2.3 Ah to 2.4 Ah. On the other hand, Sample 4 of Example 2 wastested under the same conditions, the discharge reserve was unchangedfrom the case of a test under ordinary humidity. Therefore, it ispreferable that the uppermost surface layer of a battery that isexpected to be used in a high humidity environment is formed of a resinhaving a high water resistance.

[0067] In Examples 1 and 2, the cases in which a resin having a smallhydrogen permeability coefficient (the hydrogen permeability coefficientis 1×10⁻¹⁷ mol·m/m²·sec·Pa or less) was used were described. However,with a resin having a hydrogen permeability coefficient of 1×10⁻¹⁵mol·m/m²·sec·Pa, a sufficient effect can be obtained if the thickness ofthe coating layer is about 100 μm (hydrogen permeability: 1×10⁻¹¹mol/m²·sec·Pa).

[0068] The invention may be embodied in other forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not limiting. The scope of the invention is indicatedby the appended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. An alkaline storage battery including a batterycase and a group of electrodes arranged in the battery case, wherein thebattery case comprises a resin case and a coating layer made of a resinformed on at least one surface selected from an inner surface and anouter surface of the resin case, and a hydrogen permeability coefficientof the resin that is the material of the coating layer is 1×10⁻¹⁵mol·m/m²·sec·Pa or less.
 2. The alkaline storage battery according toclaim 1, wherein the resin of the coating layer is at least one resinselected from the group consisting of polyvinyl alcohol, ethylene-vinylalcohol copolymer, polyacrylonitrile and polyvinylidene chloride.
 3. Thealkaline storage battery according to claim 1, wherein the resin case ismade of a polymer alloy of polypropylene and polyphenylene ether.
 4. Thealkaline storage battery according to claim 1, wherein a thickness ofthe coating layer is in a range from 5 μm to 100 μm.
 5. The alkalinestorage battery according to claim 1, wherein a hydrogen permeability ofthe coating layer is 1×10⁻¹¹ mol/m²·sec·Pa or less.
 6. The alkalinestorage battery according to claim 1, wherein the coating layer isformed on an outer surface of the resin case.
 7. The alkaline storagebattery according to claim 1, comprising a multilayered film formed onthe at least one surface, wherein the multilayered film includes thecoating layer.
 8. The alkaline storage battery according to claim 7,wherein the multilayered film is integrated with the resin case byinsert molding or two-color molding.
 9. The alkaline storage batteryaccording to claim 7, wherein the multilayered film includes a surfacelayer made of a water resistant resin.
 10. The alkaline storage batteryaccording to claim 7, wherein the multilayered film includes a layercontaining a resin constituting the resin case on a surface in contactwith the resin case.
 11. An alkaline storage battery including a batterycase and a group of electrodes arranged in the battery case, wherein thebattery case comprises a resin case and a multilayered film formed on atleast one surface selected from an inner surface and an outer surface ofthe resin case, and the multilayered film includes a surface layer madeof a resin and a metal layer disposed between the surface layer and theresin case.
 12. The alkaline storage battery according to claim 11,wherein the multilayered film further comprises a resin layer disposedbetween the metal layer and the resin case.
 13. The alkaline storagebattery according to claim 12, wherein the multilayered film isintegrated with the resin case by insert molding.
 14. The alkalinestorage battery according to claim 11, wherein the resin case is made ofa polymer alloy of polypropylene and polyphenylene ether.
 15. Thealkaline storage battery according to claim 11, wherein the metal layeris made of aluminum.